1. Field of the Invention
The present invention relates to an information processing device having a display unit adapted to be capable of controlling the display brightness and a display brightness control method.
2. Description of the Related Art
In recent years, information processing devices exemplified by personal computers have become remarkably widespread and such portability as makes equipment easy to carry about has been regarded as important. Many of such information processing devices are equipped with a flat-panel display typified by a liquid crystal display. When a user carries an information processing device having such a display and uses it while moving, depending on the lightness of surroundings, the display may become less easy to view. That is, if the brightness of the display set low in light surroundings, the display will be less easily viewed because of its poor brightness. If, on the other hand, the brightness of the display set high in dark environments, it will also be less easily viewed because it is too bright.
Taking such a problem into consideration, a device has been proposed which detects the lightness of surroundings and adjusts the brightness of a display in accordance with the detected lightness (see, for example, Japanese Patent Application KOKAI Publication No. 10-228010). Such a device is particularly useful for portable electronic equipment because the display brightness is automatically controlled in accordance with the lightness of surroundings. In addition, a technique has been proposed which, in changing the display brightness depending on which of mains power supply and battery pack is used, gradually changes the brightness (see, for example, Japanese Patent Application KOKAI Publication No. 2001-184046, pp. 7-10, FIG. 3A).
With the above information processing device equipped with the automatic brightness adjustment mechanism, it is easy to handle at the time of usual use because the display brightness is automatically adjusted according to the lightness of surroundings. However, if the lightness of surroundings were changed frequently and the display brightness were changed correspondingly, the user would feel visual fatigue.
In the technique to gradually change the display brightness when the brightness is varied according to the type of power supply used as disclosed in Japanese Patent Application KOKAI Publication No. 2001-184046, the user can switch power supplies between AC power supply and battery pack at will but cannot intentionally change the display brightness. Each time a person passes by the personal computer and it is shaded by the person, the display brightness will be changed frequently, which will give a strong visual stimulus and tired feeling to the user.
As described above, the brightness adjustment mechanism, which automatically controls the display brightness according to the lightness of surroundings, has a problem with respect to use in places with varying degrees of lightness.